Saves approx 1 mpg and my driving is 25/75% city/hwy. It sometimes may flip back on if the battery isn't fully charged...I suspect this may have to do with the fact that I have a crank pulley (may not be fully running alternator), so I just keep the feature turned off.

Not that I even have this feature.. But it's been out in place by a team of engineers with far greater understanding of these cars than we have, so I don't think it will do any major harm to the car and the net is positive.

Saves approx 1 mpg and my driving is 25/75% city/hwy. It sometimes may flip back on if the battery isn't fully charged...I suspect this may have to do with the fact that I have a crank pulley (may not be fully running alternator), so I just keep the feature turned off.

The dealer rep told me if you don't lock the doors and keep the key fob more than 30 meters away, the car's computer will not fully turn off. Then the stop/start won't try to turn the car off due to low battery. I don't know if he is right, but my stop/start only intermittently works.

I use the feature quite regularly when I can. The "when I can" part was added because the BMW engineers in their infinite wisdom tie start/stop function to the icing/snowflake function (37 degrees F), even with a fully warmed up engine, so that means in Chicago it's basically unusable December to March (even though the highs occasionally get above 37, for typical 8am/6pm commute times, it's rare). Couple that with shutoff of the feature when it's too hot (I think it's somewhere in the 70-80s), I figure I only get 50% usage of the feature.

That said, there's obviously a lot of tech that goes into deciding when it engages, so you don't need to worry about it auto-stopping a cold engine for instance, and the starter has apparently been uprated for the additional usage. Also, this feature has been in use in Europe for far longer than it's been showing up in American cars (other than hybrids), and if it was causing issues, they'd know by now and correct or stop using the feature.

The value of auto start/stop definitely depends on your commute. For mostly highway drivers, it's pretty much worthless, but if you have a city commute with some long lights, it will absolutely save some gas. It also seems to be very well integrated with DCT, but might be more annoying with 6MT. It will only stop the engine and stay stopped if you keep your foot on the brake, which makes it easy to alter your behavior based on whether you think you'll be at the light long. If you are, keep braking; if not, you can brake enough to stop your car then take your foot off the brake. In the DCT, the car won't move, and the engine will never stop. Also, if your light is getting "stale", or you see the opposing light turning red, take your foot off the brake, and the car restarts. Even in instances where I haven't "prestarted" the car, it restarts so quickly that I've never had much of a delay from the restart.

In short, I find the feature to be very useful at times, albiet limited by what I view as a serious flaw of shutting it off at 37 (I think it could easily be lower, as long as the engine is warmed up), which seriously limits its applicability in colder climates, and probably limits real world fuel savings to far below estimated.

Agree. With due respect to all the responsible reasons why Auto Start/Stop is a good thing, a quiet M3 on the street is not what I signed up for....

You could always get a CD of engine sounds and pipe it into the cabin to make up for it. Oh, wait, it seems like I've heard that somewhere before and it seems to have not been an entirely popular idea.

I use the feature quite regularly when I can. The "when I can" part was added because the BMW engineers in their infinite wisdom tie start/stop function to the icing/snowflake function (37 degrees F), even with a fully warmed up engine, so that means in Chicago it's basically unusable December to March (even though the highs occasionally get above 37, for typical 8am/6pm commute times, it's rare). Couple that with shutoff of the feature when it's too hot (I think it's somewhere in the 70-80s), I figure I only get 50% usage of the feature.

That said, there's obviously a lot of tech that goes into deciding when it engages, so you don't need to worry about it auto-stopping a cold engine for instance, and the starter has apparently been uprated for the additional usage. Also, this feature has been in use in Europe for far longer than it's been showing up in American cars (other than hybrids), and if it was causing issues, they'd know by now and correct or stop using the feature.

The value of auto start/stop definitely depends on your commute. For mostly highway drivers, it's pretty much worthless, but if you have a city commute with some long lights, it will absolutely save some gas. It also seems to be very well integrated with DCT, but might be more annoying with 6MT. It will only stop the engine and stay stopped if you keep your foot on the brake, which makes it easy to alter your behavior based on whether you think you'll be at the light long. If you are, keep braking; if not, you can brake enough to stop your car then take your foot off the brake. In the DCT, the car won't move, and the engine will never stop. Also, if your light is getting "stale", or you see the opposing light turning red, take your foot off the brake, and the car restarts. Even in instances where I haven't "prestarted" the car, it restarts so quickly that I've never had much of a delay from the restart.

In short, I find the feature to be very useful at times, albiet limited by what I view as a serious flaw of shutting it off at 37 (I think it could easily be lower, as long as the engine is warmed up), which seriously limits its applicability in colder climates, and probably limits real world fuel savings to far below estimated.

This was very useful. I have tried it out for the past several days, and it is really smooth with no shuddering at all when the engine shuts off or turns back on.

I think it's a good feature in theory but in practical use it's awful. I used to try to use it but gave up pretty quickly. Too many shutdowns when I needed to move again right away and most of my commute is on a cold car so it didn't even work until warmed up. Having no engine running while at a stop never bothered me though. We also have it on our X1 and I had the dealer reset to default last setting instead of ON. We leave it off at all times.

You could always get a CD of engine sounds and pipe it into the cabin to make up for it. Oh, wait, it seems like I've heard that somewhere before and it seems to have not been an entirely popular idea.

I don't use it. I don't buy that BMW researched the extra wear on parts either.

I think they have - different starter which is MUCH more beefy than the standard one, and different alternator. There's nothing else really that would be affected by the start/stop feature.

Using mine today - for fun - it turned off exactly where I stopped for my destination. I got out of the car while it was off, took a few things out of the trunk to give to the passenger I was dropping off, and then went back in the car. Put my foot on the clutch, and I got a bling and a message I have never seen before on the iDrive, accompanied by the start stop symbol with "OFF" under it in the cluster. Damn this car is too smart. It works perfectly on my 08 although I never really use it. I do intend on switching the alternator and starter at some point to fully complete the retrofit.

It's also a very voltage sensitive feature. If your battery is not in tip-top shape it won't turn off the engine.